To begin, preheat your oven to 325 degrees. Grease and flour a 9x13 baking dish and set it aside.
In a bowl, stir together the flour and baking cocoa. Set aside
In your mixing bowl, beat the eggs and sugar together. Stir in hazelnut extract, butter, and Nutella until smooth. Mix in the flour mixture, stirring until just combined. Spread the brownie batter evenly in your baking dish.
For the Cheesecake
In a clean mixing bowl, beat the eggs until frothy. Mix in the cream cheese until smooth. Stir in the sugar and Nutella until smooth. Pour the cheesecake over the brownie and spread it smooth.
Bake 50-55 minutes until the cheesecake is set and firm. Cool on a wire rack until it is room temperature. Cover it and chill it in the fridge for at least 3 hours or more.
Cut a serving and give it a light dusting with powdered sugar.